Influence of Body Position on Cardiovascular Changes during Isometric Exercise

A group of seven male participants [aged 22,9 (SD = 0,9) years] twice performed, a two-leg extension effort lasting a total of 4 minutes with a 30% intensity of maximal voluntary contraction (MVC), in the sitting (ST) and two days later in the supine position (SU). At rest, during each minute of exercise and the 4 minute recovery period the following variables were measured: heart rate (HR), stroke volume (SV), cardiac output (CO) by impedance cardiography system, systolic (SP) and diastolic blood pressures (DP) by the Korotkof method. Mean arterial blood pressure (MP) and total peripherial resistance (TPR) were also calculated. It was observed that at rest the SV was significantly higher, but HR, DP and MP were lower in SU when compared to ST (p < 0,05). Moreover during exercise these indices decreased more in the SU than in ST position when compared to the resting values. HR, DP and MP were enhanced in both the tested positions, but CO and SP were significantly higher in both positions as compared to the resting values. From our study it was concluded that the adaptability of the cardiovascular system during isometric exercise is based on changes in the left ventricular afterload, different in various body position with simultaneous suppressed baroreceptor reflexes.